It was a mixed 12 months for O'Brien. On the upside, he sold off petrol station and retailer business Topaz for an estimated €450m, making a massive profit on the €150m he paid to buy the loans from IBRC in 2013.

O'Brien (57) also successfully offloaded his Chinese recruitment interests in 2015, a year after selling the European operations.

The headlines naturally focused on O'Brien's cellular operator Digicel. In the summer he announced plans to float, which would have valued it at about €9.2bn.

Unfortunately for him, the markets dived at just the wrong time and he pulled the IPO at the last second. Presumably the billionaire businessman will look at returning to the IPO route at some stage in the future.

Digicel has been a massive cash-cow for the telecoms entrepreneur and he's amassed close to $1.5bn in dividends in the last decade.

While the millions he ploughed into INM, publishers of this newspaper, are slowly regaining value, his other investments are paying off in spades. O'Brien is known to love media, though that doesn't mean he will stand back if he feels he has been wrongly treated.

One of his far-sighted acquisitions was the Quinta do Lago resort on the Algarve, which has been transformed into a luxury golfing mecca. The dealmaker rebuffed an estimated €220m offer for the resort bought for about €31m in 1998.

Services group Siteserv is also going strongly. Profits rose 80pc to €14.2m last year. It'll now be worth a multiple of the €45.5m he paid for it.

The bulk of O'Brien's fortune was generated when he built up telecoms firm Esat in the late 1990s before selling it to BT, netting about €317m in cash. In less than 17 years, he's increased his fortune 17-fold.

O'Brien has not been slow about investing it either, acquiring diverse businesses abroad, but has also been keen to invest in brand Ireland.

Apart from his radio assets, including Today FM and Communicorp, he's invested in some valuable real estate including a landmark new office block on the corner of Dublin's St Stephen's Green and Earlsfort Terrace.

He also purchased the Beacon Private hospital in Sandyford two years ago, investing in a major expansion in high tech medical facilities.

It's reported he received delivery of a new €65m Gulfstream G650ER in November, the ideal mode of transport for reaching far-flung business outposts in the Pacific and Caribbean for Digicel executives.

O'Brien lost a close friend and confidante, former government press secretary PJ Mara in January. PJ had been a member of the Digicel board.

Ballynahinch Castle in Connemara, one of the country's finest hotels, also comes under the O'Brien ownership. Retaining the heritage of the castle has been a key part of its refurbishment.

He owns many fine properties including a home in affluent Ballsbridge. Under the radar, the businessman has major philantrophic interests, funding charitable organisations abroad and back home.

Known as fiercely loyal, O'Brien has a reputation as a shrewd but tough operator. Recently, he went to court against a relatively unknown PR company over fears it was behind material designed to cause reputational damage. Friends describe a man of charisma and the ultimate international dealmaker.